Grimshaw



March 3, 1964 c. GRlMsHAw 3,123,697

THERMALLY RESPONSIVE SWITCH 3 90, orney.

2 Sheets-Sheet 2 Filed Dec. 28, 1960 United States Patent O 3,123,697TEMRMALLY liES-PUNSVE SWITCH Qlrarles Grimshaw, Fulton, lill., assignerto General Electric Company, a corporation of New York Filed Dec. 28,1960, Ser. No. '78,923 12 Claims. (Cl. 20d- 137) This invention relatesto thermally responsive switches, and more particularly, thermallyoperated switches of the type having a housing or frame whichconstitutes a thermally responsive actuating element of the switch.

Thermally operated switches having a thermally responsive housing orframe are frequently used to provide thermal protection for electricalapparatus, such as electric motors. One prior art form of such a switchincorporates a tubular member which is expansible and contractiblepursuant to predetermined variations in ambient temperature and alsoserves as a housing for the switch mechanism. Within the tubular memberof this switch there is disposed another element which is also thermallyexpansible and contractible but at a slower rate. The tubular member andthe interior element are arranged in the switch in such a manner as tocontrol a contact means, with cornpensation for the rate at which theambient temperature rises. For example, when there is a relatively rapidrise in ambient temperature, the tubular member insulates the interiorelement from the temperature change, and expands longitudinally toactuate the contact means at one temperature Value. When a gradual orslower rise in ambient temperature is sensed by the switch, the interiorelement receives the effect of the heat and expands longitudinally tocompensate for the expansion of the tubular member. The contacts arethen actuated at a higher temperature Value than the rst value due tothe compensating eiect of the interior element. Such a mode of operationin thermally responsive switches of the prior art has been commonlyreferred to as thermal anticipation.

To amplify the thermally responsive motions of the tubular member andthe interior element in such prior art switches and to actuate thecontact means thereof, various structural arrangements have beenemployed. These arrangements have proven to be complicated andrelatively expensive. in addition, the structural configuration andarrangement ofthe various parts of some of these switches havenecessitated an over-all switch structure which is relatively bulky andditlicult to install in an associated apparatus. it has, therefore, beenfound desirable to provide an improved thermally responsive switch ofthe nature described, which is extremely efficient, simple, small insize, and readily manufacturable.

it is sometimes desirable to use these switches in the same environmentas hermetically sealed apparatus, such as hermetic motors. For example,the hermetic motor might be part of a hermetically sealed compressorsystem. lin this type of environment, it has been found that extraneousfluids such as oils and gases, as well as extraneous particles, oftenproduce an adverse effect upon the longevity of the switch. lt has,therefore, also been found desirable to provide a thermally responsiveswitch which is easy to hermetically seal and thereby efficiently lendsitseliC to the association with and control of hermetically sealedapparatus.

Accordingly, it is the primary object of this invention to provide animproved thermally responsive switch which is novel in construction andvery eclent in operation.

An additional object of my invention is to provide an improved thermallyresponsive switch which provides precise and consistent actuation of thecontacts throughout the life of the switch.

Another object o-f this invention is to provide an improved thermallyresponsive switch that is hermetically sealed, relatively small in size,sturdily constructed, and has a long life.

It is a further object of my invention to provide an improved thermallyresponsive switch which is hermetically sealed, and which due to itsrelative simplicity may be manufactured at a reduced cost.

Another object of my invention is to provide an improved thermallyresponsive switch having a built-in means for compensating the switch inaccordance with the rate of ambient temperature change, and veryaccurate, but yet inexpensive, and readily assembled means for utiliningthe actuating forces from two thermally responsive members to actuatethe switch contacts.

In carrying out my invention, in one form thereof, I provide ahermetically sealed thermally responsive switch wherein switch elementsare housed within an elongated tubular member that is sealed at each ofits ends. An elongated support is positioned longitudinally within thetubular member. The tubular member and tbe support are expansible andcontractible in response to temperature Variations with the rate ofexpansion and contraction of the support lagging that of the tubularmember. A force transmission lever is also positioned within the tubularmember and it is operable between irst and second positions. An actuatoris pivotally mounted on the support and continuously engaged by thelever to amplify the movement of the lever and control a pair of switchcontacts. The actuator is continuously spring biased into engagementwith the lever to urge the lever toward its lirst position. The leverincludes a force receiving section disposed transversely near one end ofthe tubular member and near one end of the support. One side of theforce receiving section engages the adjacent end of the tubular memberat a lirst pivot, and the other side of the section engages the adjacentend oi the support at a second pivot which is spaced transversely fromthe Iirst pivot. The tubular member and the support are arranged toexert offset and oppositely directed thermally responsive compressiveforces upon the lever at the iirst and second pivots respectively.rlhese compressive forces tend to move the lirst and second pivots inopposite longitudinal directions and are normally of suflicientmagnitude to retain the lever in the .second position against the forceexerted thereupon by the spring biased actuator. When the ambienttemperature increases, the tubular member expands longitudinally to movethe lirst pivot and diminish the compressive force exerted upon thelever by the tubular member. When the rate of rise in temperature allowssutiicient ambient heat to be sensed by the support, the support alsoexpands longitudinally. The expansion of the support moves the secondpivot and thereby increases the compressive force exerted upon the leverby the support. This movement of the second pivot lags the movement ofthe rst pivot but partially compensates therefor, to provideconipensatio-n in the switch for the rate of temperature rise. Bytransmitting tne thermally responsive forces of the tubular member andthe support to the lever through the pivots and amplifying resultantmovements ot' the lever to operate the switch contacts through thepivoted and spring biased actuator, a very eflicient switch with preciseand consistent actuation of the switch contacts is thereby obtained.

Further aspects of my invention will become apparent hereinafter, andthe specification concludes with claims particularly pointing out anddistinctly claiming the subject matter which l regard as my invention.The invention, however, as to organization and method of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description when taken inconjunction with the accompanying drawings, in which:

FIG. l is a perspective View of an improved thermally E responsiveswitch embodying my invention, with a pair of leads connected to theswitch terminals;

FIG. 2 is a sectional side view of the switch of FlG. 1I with theinsulating sleeve removed and the contacts in their normally closedposition;

FIG. 3 is a sectional view taken along the lines 3-3 as indicated inFlG. 2;

FlG. 4 is a sectional end view taken along the lines 4 4- as indicatedin FIG. 2, with the switch contacts in their closed position;

FIG. 5 is a view similar to the View of FIG. 4, but showing the switchcontacts in their open position;

FIG. 6 is an exploded view showing the structural details of the variouselements of the switch of FIG. 2;

FlG. 7 is a fragmentary view of the switch of FlG. 2 showing theassociation between the actuator, the movable Contact and the fixedcontact, when the switch contacts are in the open position;

FIG. 8 is a perspective view of the force transmission lever of theswitch of FIG. 2; and

FIG. 9 is a sectional side view of a switch embodying my invention inalternate form thereof.

Referring now to the drawings and more particularly to FlGS. 1-3, l haveshown a thermally responsive switch l wherein my invention has beenadvantageously employed. To furnish a diminutive housing for the variouscomponents of this switch, which also eiiiciently serves as a thermallyresponsive element, l have provided the tubular casing 3. In theillustrated embodiment, the size of casing 3 approximates that of acylindrical pencil having a length of less than two and one quarterinches. Contact terminal assembly 5 is welded to upper end '7 of thecasing 3 and nut 9 is welded to the lower end ll thereof (as viewed inFlG. 2) to provide a smooth anh compact hermetically sealed housing forthe various internal switch parts. To electrically insulate the housingand enable the switch to be readily inserted in the windingr of anelectric motor, as shown in FIG. l, a sleeve i3 of suitable electricinsulating material, such as Mylar, is formed around the housing. Itwill be understood that the sleeve 13 is thermally conductive and verythin and therefore has little resistance to the transfer of heat to theswitch housing. In addition, sleeve l3 is preferably thermallyshrinltable so that it may be shrunk around the tubular member 3 and nut9 in contiguous relationship-thereto. This contiguous relationshipminimizes any resistance to transfer of heat to the tubular member 3.

Turning now to a further discussion of the housing which has beenprovided for my improved switch l, casmg 3 is preferably made from ametallic material having a relatively high coeicient of expansion, suchas stainless steel or brass. Contact terminal assembly 5 includes acylindrically-shaped terminal l5 which has an annular flange ll7 formedat its irmer end. EndV of casing 3 is bent inwardly against the shoulderlo of 'annular flange 17 and welded thereto to iirst close end 7 of theswitch housing. Fixed contact terminal l@ extends axially throughterminal l5', being separated therefrom and sup-v ported therein byfused electrical insulating material 2l. Inner end 23 of the iixedcontact terminal is flattened on opposite longitudinal sides (as shownin FlG. 2) to sup-4.

port fixed contact button 25 of the switch.

To close the other end lll of casing 3, after contact terminal assembly5 has been welded to casing 3, the various parts of the switch have beenpositioned'within the housing, and the switch has been properlyassembled, nut

9 is welded to the casing, preferably by spot welding. To

hermetically seal the switch, the end lll may be dipped in moltensolder. As shown in FlG. 6,nut 9 includes a partially ring-shapedVshoulder 26' which engages the major Vportion of end ll of the casing3. Nut 9 is partially cylintom end ll of the casing after the assemblyof the various parts within the housing, for the adjustment of thetemerature differential before end ll is sealed. The structure andfunction of the flexible strip 27 shall be described in detailhereinafter. The nut 9 has a centrally disposed threaded apertureextending axially therethrough which is engaged by adjustment screw 29.This adjustment screw serves to calibrate the switch for proper responseto the thermally responsive actuating forces, as shall hercinafterbecome apparent.

Turning now to a consideration of the interior of switch l, as shown inFIGS. 2 and 3 (the separate parts being 1est seen in FIG. 6), anelongated support 3S is positioned longitudinally within switch cavity37. This support 35 serves as a second thermally responsive elementencased within the housing and is preferably constructed of steel. Moreparticularly, support 35 resembles in overall appearance, a generallyU-shaped channel, and, as shown in FIG. 6, includes elongated sides 38which are spaced apart in parallel relationship by longitudinally spacedU-shaped bight sections or ribs 39, 41, 43, 45, and 7. Stepped upperends 49 of the sides 3d compressively engage the inner surface ofterminal l5 on opposite sides of the inner end of fixed contact terminali9. (See FIGS. 2 and 3.) Rib 39 is formed at the other end of support35. As shown in FlG. 6, rib 39 includes an extension which is curvedslightly inwardly or in the direction of sides 3S and has a sharptransverse knife edge 5l formed thereon. The purpose of the ltnife edge5l is to transmit thermally responsive force variations from within theswitch housing to a motion amplifying lever assembly, as shall bedescribed hereinafter.

For pivotally supporting a switch actuating means, connecting rib il isspaced longitudinally from end rib 39 by a slot 52. A pair of lingers 53are spaced apart laterally and curved angularly inwardly from the innersurface of the upper end of rib il (FIG. 2). Fingers 53 extend angularlytoward the left side of casing 3 and upwardly away `from slot 52, asviewed in FIG. 2, having a space 54 therebetween (FIG. 6) and sharpouter edges which provide a pair of knife edge supports for switch actu-Y ator 55.

Vare spaced apart longitudinally by the slots 59 and 6l.

Elongated bight section 65 Vextends between slot S9 and the bottom end63 of the actuator. Section 65 has formed therein a centrally disposedlanced tab 67 and m adjacent stamped embossment 69. The free end of tab67 extends angular'ly upwardly and to the right (viewing FIG. 2).Fmbossrnent 69 has the configuration of a D-shaped plateau on the rightside thereof (FIG. 2). The bottom side of this plateau provides a pairof spaced apart transverse shoulders 7l (FIG. 6) which face toward end63 of the actuator and are spaced slightly longitudinally upwardly fromthe free end of the tab 67 (FlG. 2). Shoulders '7l provide sharp inneredges which are transversely and linearly arranged.

Actuator 'is positioned on the left side of the ribs of support 35'(viewing 2) with knife edges 53 of the Vsupport each linearly` engagingbeneath and against an associated one of tle actuator shoulders (Seealso FIG. 6.) The yfree end of lanced tabV prc-iectsV angularly to theright, as shown in 2, and traverses between the lni ders '7l upon theirassociated knife edges 53. The engagement of Vactuator shoulders El withknife edges 53 of the support thusrprovides an accurate pivotal supportedges 5S to laterally position the shoul- 35, L-shaped tab 72 of thesupport extends transversely to the left (PEG. 2) through slot 59 of theactuator and then upwardly, parallel to rib 43. The free end of tab 72is thus positioned to the left of the bottom end of actuator bightsection 66 to limit pivotal movement of the actuator in acounterclockwise direction of rotation.

To properly balance actuator 55 upon its pivots, a weight 73 of suitablemagnitude is welded to the right side or bight section 65, as viewed inFIG. 2. In order to provide clearance for pivotal movement of theactuator 55 near bottoni end @3 thereof, weight 73 lies generally withinslot 52 of the support.

To operate the contacts of my improved switch l, and thereby control anexternal circuit, the upper end of actuator 55 (as shown in FlG. 2) isspecially formed to pivotally support and carry movable Contact strip7S. (See also HG. 6 and FIG. 7.) More particularly, bight section 63 ofactuator 5S has an embossed spring seat '79 formed thereon whichprojects to the left, as shown in FIG. 2. An L-shaped extension 8l isformed on an upper prolongation of section d. This extension 8l includestransverse portion 83 and a switch actuating arm 85 which extendslongitudinally within cavity 37 on the left side of fixed contact button(FIG. 2).

To efficiently guide and pivot movable contact strip 75 upon actuator55, the strip 75 includes a channelshaped section S7 and achannel-shaped contact extension Strip 75 is preferably formed from athin strip of silver metal. The longitudinal axes of section d'7 andextension d@ of the strip are generally perpendicular to each other.Opposed sides 9i and 93 of extension 89 are parallel to each other andspaced apart to allow a suitable wipe distance for movement of the freeend 95 or the actuator therebetween. The sides of channel section S7serve to position the movable Contact strip laterally relative to theactuator', as shown in FIG. 3.

Movable contact strip 7S is positioned upon the L- shaped extension ofthe actuator 55, as shown in FIGS. 2 and 7, with transverse portion S3of the actuator extending through slot gli of the contact strip. Freeend iti of arm S5 of the actuator is then disposed to the left ofextension side @Si between it and side 911. Movable contact button 97 isembossed on the right side of contact extension S9 and disposed oppositeto xed contact button 25.

To normally bias movable contact button 97 toward iixed contact button25 and provide a wiping action, as will be hereinafter explained,embossed spring seat 599 is formed in the bight portion of channelsection 87. Seat il@ is positioned so as to face seat 79 of theactuator. (See FIG. 7.) Spring itil runs in compression between theoppositely disposed seats 79 and 99 of the actuator and movable contactstrip, respectively, to normally urge movable contact button 97 in aclockwise direction of rotation (viewing FIG. 7), the strip 75 pivotingat slot 9d around transverse actuator portion 83. When the switchcontacts are closed, end 95 of actuator 5:5 is in engagement with side93 of the movable contact strip 75. Spring lidi is then held incompression, as shown in FlG. 2, by the sandwiching of side 93 and themovable contact button @7 between actuator end 95 and rigid fixedcontact 2S.

In order to provide snap action for the switch contacts of switch l, lhave provided U-shaped toggle spring This spring is in continuouscompression between pivot edge ldd of llexible strip 27, and transverseprojecting edge M37 which is formed on an upper extension of actuatorbight section 66. Edges ld and M97 of the actuator 55 and strip Z7,respectively, engage indented end portions of the toggle spring 1;@3, asshown in FIG. 7, to etlect the snap action of the actuator about itspivots 7l. Spring iltl pivots about strip edge M95 and continuouslybiases actuator 55 in the direction of the open position of the switchcontacts7 or with a counterclockwise moment of biasing force aboutpivoting shoulders 7l of the actuator.

To facilitate the adjustment of the biasing force applied to the switchactuator 55 by the toggle spring M3, after the various parts of mydiminutive switch l are assembled within tube 3, the aforementionedtlexible strip 27 is stretched in tension between the support rib 47 andthe bottom end of the casing 3, as shown in FlG. 2. The particularconstruction of strip 27 and its arrangement in the switch cavity foradjusting the biasing force transmitted to the actuator by toggle springlr03, comprises the invention ot Edward O. Andersen, and thisconstruction and arrangement are described and claimed in his copendingapplication Serial No. 78,922 led concurrently herewith and assigned tothe same assignee as the present invention. As shown in FIG. 6, strip 27is elongated, and at its upper end, it has an enlarged rectangularsection i169, with a rectangular slot lll formed therein. To attachstrip 27 to the support, the end of the strip near which slot lill isformed is extended outwardly, perpendicularly away from, and then backparallel to the principal surface of the strip to provide a generallyhooked-shaped fold M3. Fold 11.3 is wrapped around rib i7 of thesupport, as shown in FIG. 2, before the assembly of the switch partswithin the housing. Bottom end i115, with a tool aperture therein, isextended out of the housing over the flat surface 9a of nut 9 and ispulled to vary the position of pivot edge lltS longitudinally anddownwardly. This movement of pivot edge i635 provides the desiredcompression for spring 103. The bottom of the strip is then weldedbetween the right side of nut 9 and the adjacent bottom end ll of thecasing (FlG. 2) to set the spring biasing force at the desiredtemperature differential for the switch. Rectangular slot lill providesclearance for the movement of both of the free ends oi the toggle springw3. Intermediate the ends of the strip Z7, an outwardly raised surfaceM7 is projected toward the wall of the casing to help position the strip27 within the casing and guide the longitudinal movement ol the strip.lt will thus be seen that the structure of strip 27 allows convenientadjustment of the biasing force imparted to actuator 5S by toggle springitl?) after the assemblage of the switch parts within cavity 37.

Turning now to an important aspect of my invention, which is theprovision in my improved switch of an efcient and accurate means foroperating the actuator and conta ts there-oiC by two thermallyresponsive members in the lower portion of switch cavity 37, l havepositioned a force transmission lever H9. Considering lirst thestructure of lever lll, as shown in FG. 2, it includes a force receivingsection lit-l, an elongated force transmission section which extendsperpendicularly upwardly from the left side of section Ml, and anactuating section lES which extends angularly from the upper end ofsection 123 toward the upper end of the recess formed by embossment d@in the actuator' 55. rThe outer side of force receiving section lZll, asbest illustrated in PEG. 8, has a V-haped knife edge l27 projectingoutwardly therefrom. This edge i127 is accurately formed so that it isperpendicular to the longitudinal center line of lever M9 (as may beseen in FIG. 3). On the opposite or inner side of force receivingsection lil, and spaced between edge 127 and the adjacent right end ofthe lever (FlG. 2), a shallow V-shaped groove 129 is formed. Theinnermost extremity ot this groove is accurately parallel to the knifeedge 3.27 and also perpendicular to the longitudinal center line of thelever lll@ (viewing FlG. 3).

Lever litt is assembled within switch cavity 37 with a right-angled shiml3l overlying the adjacent outer surfaces of force receiving section lZland section i123. The inner end of adjustment screw 29 has afrusto-conical shape and it engages the outer side of leg i312 of theshim. The inner side of the shim leg i3?. is sharply engaged by knifeedge 127 of force receiving section 312i to imbed a knife edgedindentation therein. The engagement of knife edge E27 with shim leg l32provides an accurate pivotal relationship between the housing of theswitch and lever il? which is precisely preserved during th rotation ofsc ew by the engagement of the legs of th. shim with the adjacent outersurfaces of sections l2 and 123.

The transverse knife edge 5l of support 55 pivotally engages the shallowgroove M9. Support runs in compression between annular tlc-.nge l? atthe upper end of cavity 37 and groove 31.2% of lever section It willthus be seen that force receiving section 1.2i of lever il@ is incornpressive engagement with the switch housing Vby means of screw 29,sl iin jlll, and the V-shaped knife edge l 7, and it is also incompressive engagement with the support by means of knife edge 5l andgroove 129. The oilset points l2? and l2@ of the lever thus receivecompressive forces from the lions-- ing and support, respectively. Eachof these cor-apres sive forces urges the free end of actuating section125 of the lever to rotate in a clockwise direction ot rotation, as shwn in FIG. 2, about the pivot which is coinpressed by the other force.For exarnple, the compressive arrangement of support 35 within theswitch cavity 37 imparts a compressive force to groove l2@ of the lever.This compressive force urges the free end of actuating section 125 torotate in a clockwise direction of rotation about knife edge l2?. Thecompressive force imparted to knife edge llZ by screw 29 through theshirn 1.3i urges the free end or" actuating section 125 ot the lever torotate in a clockwise direction about pivot point 129. By arranging thepivotal engagement of the housing and support with lever T119 in thismanner, precise and very efficient thermally responsive operation of theactuator is thereby achieved. A thermally responsive elongation or"approximately only a few ten thousandths of an inch will eiilcientlyactuate the switch contacts by nieans of a very high motionarnpliiication.

Turning now to a detailed description of the oper tion of my improvedthermally responsive switch lt, as shown in PEG. 2, movable contactbutton 97 is in its normally closed position, in engagement with iixedContact button 25. With the contacts of the switch in their normallyclosed position, the compressive forces imparted to lever M9 at pivots127 and 12,9 by the housing and the support are of sullicient magnitudeto hold actuator in its closed position against the biasing force or"toggle spring ldd. With the switch contacts in this position, a maiorelectric current path is provided through the switch from thecylindrically-shaped terminal .l5 to the contact terminal. l), throughthe support 35, the actuator 55, the movable Contact strip 75, and thecontact Vbutton 25. The other conductive parts ot switch, such as thecasing and lever, forirl parallel pv.. to a portion of the maior path,but whatever path is sidered, the contacts and 25 will open it when areseparated. Y

Let us suppose that nig/improved switch l is connected to the controlcircuit of an apparatus, such as a hermetically sealed motor andsupported at upper end 7 of casing 3. T he housing of the switch iselectrically insulated frorn its external supporting environmenfby Vtheaforementioned sleeve i3. When a relatively high rate of ambienttemperaturV occurs, the tubular casing 3 senses'this rapid temperaturevariationconsiderably laster than the support 35, due to the shieldingell/ect the housing has upon the support. The thermal expansion orcontraction of the support always lags that of the tubular rnernber 3for an increaseor decrease in ternd peratur l With a relatively highrate of increase in perature, the bottom end lll oi the tubo expandslongitudinally downwardly a few ten thcusandths of an inch Vtroni whereit is shown in lllG. 2. llut l and Vscrew 29 also rnove downwardly'withVcasing 3, since Cai aes?

compressive force at knife edge 127,. actuating section 125 of leverlli? is ultimately (ie, at the value of the predetermined ultimate triptemperature) allowed to inove in a counterclocltwise direction ofrotation (viewllG. 2) by the counter'cloclowise biasing force exertedthereupon by the spring biased actuator rThis motion causes actuator S5to inove in a ccunterclocltwise direction of rotation about its pivots.As best sh wn by a comparison or FIG. 2 and 'FIG'. 7, the biasing torceof toggle spring ld?) nieves the free end or" the actuator away frominner side 93 of the movable contact extension toward outer side Elthereof. As the free end of the actuator begins to niove away from sidetoward side Gl, the compressive force applied by spring ll to themovable contact strip urges the movable contact b tton to rotate in aclockwise direction. Spring lbl thus retains contacts in engagementuntil the free end 9:3 of the actuator has traveled the wipe distance(i.e., the approximate distance bet een the inner surfaces ot sides nland 93 rninus the thickness or the actuator at its free end @5). Thefree end 95 of the actuator then engages side @l of the movable contactstrip and thereby pivots the movable Contact button 97 out oi engagementwith the lined contact button 25 (HG. 7). This is the open contactsposition for the switch. After the switch contacts have been opened, wh.i the tubular rneinber 3 is cooled, it contracts and thereby diminishesin length. With the occurrence of this teinperature condition, levereventually receives a si cient compressive force at pivot M7 front theswitcn housing to overcome the spring biased actuator and reclose thecontacts.

Supposing now that my irnproved switch ll is exposed to a relatively lowrate of increase in temperature, when this ambient condition ccurs, thetubular casing 3 and support 3L each expand longitudinally in the sainedirection, downwardly as shown in FIG. 2, or away from the contact endof the housing. The containment of support 35 by the switch housing hasless effect upon transfer of heat to the support for this condition andsupport 35 receives a signiiicant eiect from the therrnal variation.Tubular casing 3 thus expands longitudinally a few ten thousandths of aninch, with support 35 ei;- panding longitudinally in the direction, butto a lesser degree. The compressive force exerted upon knife edge l2? orthe lever by screw Z9 is then reduced by the thermal expansion of casing3, but at the saine time, the cornpressive force urged upon pivot grooveof the lever by support 35 is gradually increased by the therinalexpansion of the support. lt v i thus be seen that the thermal expansionof support 35 partially cornpensates for the thermal expansion oftubular casing when the rate of rise in temperature is low enough toallow significant transier of heat into cav y of the casing. Since thethermally responsive compressive force urged upon lever lili? oy support35 increases in response to temperature rise and partially compensatesfor the diminishing of the compressive force exerted upon lever by thehousing when there is a elatively slow tei.,- perature rise in lieu of arelatively rapid temperature rise,

Y it is necessary for the ambient temperature to reach a derpredetermined value before the contacts of the switch will open. Whenthis higher predetermined ten.- perature value has Vbeen reached,actuator ol the switch will open the contacts in the saine manner. aspreviously described'for the relatively high rate or teinperaturevariation.

=lt will thus be seen that l have `provided a new and improved thermallyresponsive switch which provides compensation for rate of temperaturerise. rfhis switch provides an eicient Iand very `accurate motionampliiication systern for operating a pair ofV switch contacts bythermally responsive compressive forces from a tubular casing and aninner support.l By mounting the force transmission lever in precisepivotal ,engage-ment. with 9 the support and the tubular member, aninexpensive and readily Aassembled means for transmitting the actuatingforce from the thermally responsive members to the contact actuator hasbeen thereby achieved. My switch also incorporates a very effectivemeans for snapping the switch contacts between their open and closedpositions.

FiG. 9 illustrates, as a modified form of my invention, a thermallyresponsive switch ido. For switch Mtl, the same reference numerals havebeen employed to indicate switch parts that have heretofore beendescribed for switch l. Parts which have a modified structure incomparison to the structure of their correlativo parts in switch ll butperform the same basic functions in the switch lll@ are identified bythe same reference numeral with the letter a sufixed thereto.

To eliminate some of the manufacturing tolerances which would occur inmaking my improved switch, support 35a has an upper end rib 142 (asshown in FIG. 9) with tab portion lll/11 formed thereon. rllab portion141 extends singularly downwardly and away from the bottom side of ribridi?. toward the adjacent inner wall of casing 3. rllhe free end of tabportion Ml labuis the casing Wall to force the upper end of support 35alaterally toward the left side of the casing and thereby reduce thebuilding up of tolerances during the manufacturing operation for theswitch ilih. To facilitate clearance for the right side of fixed contactbutton (FIG. 9), when the upper end of support a is positioned in thecavity of switch ld@ by tab portion Mi, aperture M3 is formed directlyto the right of contact button 25.

in order to hermetically seal the ybot-tom end of switch ifitb, it willbe noted that nut ldd therof is smaller than nut 9 of switch i and isfitted inside of casing 3 near its bottom. Nut M4 has the same D-s'napedconfiguration as nut 9, but the cylindrical peripheral portion thereofis smooth. A. special yflat protuberance 147 is formed on the `fiatright side of nut litri. Nut ddd is 4welded to the inner wall of thecasing 3 at ldd. Protuberance ill-i7 extends longitudinally in a planeparallel to the axis of screw Z9, and it serves as a supportingprojection for receiving the weld of flexible strip 27a after thetemperature differential has been properly set. Free end Ild@ offlexible strip 27a is then looped transversely within the bottom ofcavity 37 outwardly of screw 29. After screw 29 is properly adjusted tocalibrate the compressive forces exerted upon lever li?, it is welded tonut ldd at Cup-shaped cap lldll is then pressed into its position, asshown in FIG. 9. Cap iSll is flush with the edge of the tube and thesmooth surface of its annular rim 153 engages the inner wall of thecasing near its bottom. The cap lSl is then welded to the casing,preferably by the heli-arc method, to hermetically seal the switch ldfi.

Operationally, the modified form of my invention is identical to thearrangement of switch l which has been previously described.

The simplicity of my improved switch permits the dimensions to be smallcompared to other prior `art devices affording su@ action of the switchcontacts, and provides a structure which is readily hermeticallysealaole. For example, in a thermally responsive switch constructed inaccordance with this invention for protecting electric motors of from lto ltlOl horsepower, the device has an over-all length of 3 inches, anda diametrical width of approximately .276 inch.

While in accordance with the patent statutes, l have described what atpresent are considered to be the preferred embodiments of my invention,it will be obvious to those skilled in the art that various changes andmodifications may be made therein without departing from the invention,and l, therefore, aim in the following claims to cover all suchequivalent variations as fall within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

il. A thermally responsive switch comprising an elongated housing, anelongated support disposed longitudinally Within and substantiallycontained by said housing, said housing and said support each beingexpansible and contraotible longitudinally in response to temperaturevariations md at respectively different rates: with the rate of responseof the support lagging that of the housing, lever -means disposed withinsaid housing 4and operable between first and second positions, switchcontact means disposed within said housing and operable by said levermeans, fixed contact means engaged by said switch contact means whensaid lever means is in said second position, and resilient meanscontinuously biasing said lever means toward the first position, saidlever means including a force receiving section disposed `transverselywithin said housing, one side of said section engaging said housing `ata first pivot, the other side of said section engaging said support at asecond pivot spaced from said first pivot, said housing and supportbeing arranged to exert offset and oppositely directed thermallyresponsive forces upon said lever means at said first and second pivotsrespectively to normally urge said lever means into the second .positionagainst the biasing force of said resilient means, the movement of saidpivot points upon predetermined temperature conditions being arranged toallow said resilient means to move said lever to said first position,and said resilient means applying an increasing force as said levermeans moves :from said second position to said first position, therebyto produce a positive temperature differential between said positions ofsaid lever.

2. A thermally responsive switch comprising an elongated housing, `anelongated. support disposed longitudinally within and substantiallycontained by said housing, said housing and said support each beingexpansible and contractible longitudinally in response to temperaturevariations with the rate of response of the support lagging that of thehousing, lever means disposed Within said housing and operable betweenfirst and second positions, switch Contact means disposed within saidhousing and operable by said lever means, fixed contact means engaged bysaid switch contact means when said lever means is in said secondposition, `and snap acting resilient means continuously biasing saidlever means toward the first position, said lever means including aforce receiving section disposed transversely within said housing, oneside of said section engaging said housing at a first pivot, the otherside of said section engaging said support `at a second pivot spadtransversely from said lfirst pivot, said housing and support beingarranged to exert offset and oppositely directed thermally responsiveforces upon said lever means `at said first and second pivotsrespectively to tend to move the pivots and normally urge said levermeans into the second position against the biasing force of saidresilient means, the movement of said pivot points upon predeterminedtemperature conditions being arranged to allow said resilient means tomove said lever lto said first position, and said resilient meansapplying increasing force as said lever means moves from said secondposition to said first position, thereby to produce a positivetemperature differential between said positions of said lever.

3. A thermally responsive switch comprising an elongated tube and anelongated support disposed longitudinally within said tube, said tubeand said support being expansible and contractible longitudinally inresponse to temperature variations with the rate of response of thesupport lagging that of the tube, a lever member disposed within saidtube and operable between first and second positions, an actuatorpivotally mounted upon said support and continuously engaged by saidlever, switch contact means disposed within said tube and operable bysaid actuator, and snap acting resilient means continuously alsace? Y ll biasinT said actuator to urge said lever toward the first position,said lever member including a force receiving section disposedtransversely within said tube, one side of said section engaging saidtube at a first pivot, the other ide of said section engaging saidsupport at a second pivot spaced transversely from said first pivot,said tube and support being `arranged to exert oiiset and oppositelydirected thermally responsive forces upon said lever member at first andsecond pivots respectively to tend to move the pivots and normally urgethe lever member into the second position against the biasing force ofsaid resilient means, the movement of said pivot points uponpredetermined temperature conditions being arranged to allow saidresilient means to move said lever to said first position.

4. A thermally responsive switch comprising an elongated tube and anelongated support disposed longitudinally within said tube, said tubeand said support being expansible and contractible longitudinally inresponse to temperature variations with the rate of response of thesupport lagging that of the tube, a lever member disposed within saidtube and operable between iirst and second positions, an actuatorpivotally mounted upon said support and continuously engaged by saidlever, switch contact means disposed within said tube and operable bysaid actuator, and snap acting resilient means continuously biasing saidactuator to urge said lever toward the first position, said lever memberincluding a force receiving section disposed transversely within saidtube, one side of said section compressively engaging an inner end otthe tube at a first pivot, the other side of said section compressivelyengaging one end of the support at a second pivot spaced transverselyfrom said first pivot, said tube and support being arranged to exertoflset and oppositely directed thermally responsive forces upon saidlever member at said first and second pivots respectively to tend tomove the pivots longitudinally in opposite directions and normally urgethe lever member into the second position against the biasing force ofsaid resilient means, the movement or said pivot points uponpredetermined teinerature conditions being arranged to allow saidresilient means to move said lever to said first position.

5. A thermally responsive switch comprising an elongated tube and anelongated support disposed longitudinally within said tube, said tubeand said support being expansible and contractible longitudinally inresponse to temperature variations with the rate of response of thesupport lagging that or the tube, a lever member disposed within saidtube and operable between first andV second positions, an actuatorpivotally mounted upon said support and continuously engaged by saidlever, switch contact means disposed within said tube and operable bysaid actuator, said switch contact means including a movable contactpivotally mounted upon said actuator and carried thereby, and snapacting resilient means continuously biasing said actuator to urge saidlever toward the first position, said lever member including a forcereceiving section disposed transversely within said tube, one side ofsection engaging said tube at a lirst pivot, the other sine of saidsection engaging said support at a second pivot spaced transversely fromsaid first pivot, said tube and support being arranged'to exert offsetand oppositely directed thermally responsive forces upon said levermember at llrst and second pivots respectively to tend to move thepivots and normally urge the lever member into the second positionagainst theY biasing force ofsaid remeans, the movement of said pivotpoints upon predetermined temperature conditions being arranged to allowsaid resilient means to move said lever to said first p sition. Y

' 6. The switch or claim 5 including a compression spring extendingbetween the actuator andthe movable contact to normally ,bias themovable contact toward a fixed contact and provide a wiping action forthe switch contact leans. f f e 7. The switch of claim 5 including asleeve of electrical and thermally conductive insulating materialsubstantially surrounding the tube, said sleeve being thermallyshrinkable and-substantially contiguous to said tube, thereby toelectrically insulate the switch from an external supporting environmentwhile providing little resistance to transier of heat to said tube.

8. A thermally responsive switch comprising an elongated tube and anelongated support disposed longitudinally within said tube, said tubeand said support being expansible and contractible longitudinally inresponse to temperature variations with the rate of response of thesupport lagging that of the tube, an adjusting means mounted in saidtube, a lever member disposed within said tube and operable between rstand second positions, an actuator pivotally mounted upon said supportand continuously engaged by said lever member, switch Contact disposedwithin said tube and operable by said actuator, said switch contactmeans including a movable contact pivotally mounted upon said actuatorand carried thereby, said lever member, actuator', and movable contactconstituting a balanced lever system in said switch, and snap actingresilient means continuously biasing said actuator to urge said levertoward the first position, said lever member including a force receivingsection disposed transversely within said tube, one side of said sectioncompressively engaging the adjusting means of said tube at a rst pivot,the other side of said section compressively engaging said support at asecond pivot spaced transversely from said first pivot, said adjustingmeans and support being arranged to exert oflset and oppositely directedthermally responsive forces upon said lever member at said lirst andsecond pivots respectively to tend to move the pivots and normally urgethe lever member into the second position against the biasing force ofsaid resilient means, the movement of said pivot points uponpredetermined temperature conditions being arranged to allow saidresilient means to move said lever to said first position, saidadjusting means being linearly movable to vary the compressive forcesimparted to said lever by said tube and said support thereby tocalibrate said switch.

9. A hermetically sealed thermally responsive switch comprising anelongated tube and an elongated support disposed longitudinally withinsaid tube, said tube and said support being expansible and contractiblelongitudinally in response to temperature variations with the rate or"response of the support lagging that or the tube, said tube having apair of oppositely disposed open ends, closure means for hermeticallysealing each of the open ends of said tube, a lever member disposedwithin sai tube and operable between rst and second positions, anactuator pivotally mounted upon said support and continuously engaged byVsaid lever, switch contact means disposed within said tube and operableby said actuator, snap acting resilient means continuously biasing saidactuator to urge said lever tov/ard the lirst position, said levermember including a force receiving section disposed transversely Vwithinsaid tube, one side of said section engaging -said tube at a rst pivot,the other side of said section engaging said support at a second pivotspaced transversely from said first pi ot, said tube and support beingarranged to exert offset and oppositely directed thermally responsive-forces upon said lever member at said iirst and second pivotsrespectively to tend to move the pivots and normally urge the levermember jinto the second position against the biasing force of saidresilient means, the movement of said pivot points upon predeterminedtemperature conditions being arranged'toV allow said resilient means'tomove said lever to said nrst position. t

l0. AY thermally responsive switch comprising an elongated tube and anelongated support disposed longitudinally withinsaid tube, said tubesaidY support being expan'sible and contractible longitudinally inresponse to temperature variations with the rate of response of thesupport lagging that of the tube, a lever member disposed within saidtube and operable between iirst and second positions, an actuatorpivotally mounted upon said support and continuously engaged by saidlever, switch contact means disposed within said tube near one endthereof and operable by said actuator, a snap acting U-shaped togglespring continuously biasing said actuator to urge said lever membertoward the first position, said lever member including a force receivingsection disposed transversely within said tube near the other endthereof between said other end and an adjacent end of the support, oneside of said section compressively engaging said other end of the tubeat a irst pivot, the other side of said section compressively engagingsaid end of the support at a second pivot spaced transversely from saidfirst pivot, said tube and support being arranged to exert offset andoppositely directed thermally responsive forces upon said lever memberat said rst and second pivots respectively to tend to move the pivotslongitudinally in opposite directions and normally urge the lever memberinto the second position against the biasing force of said togglespring, the movement of said pivot points upon predetermined temperatureconditions being arranged to allow said resilient means to move saidlever to said iirst position.

11. A thermally responsive switch comprising an elongated tube and anelongated support dispose longitudinally within said tube, said tube andsaid support being expansible and contractible longitudinally inrekspouse to temperature variations with the rate of response of thesupport lagging that ot the tube, a lever member disposed within saidtube and operable between iirst and second positions, an actuatorpivotally mounted upon said support and continuously engaged by saidlever, switch contact means disposed within said tube near one endthereof and operable by said actuator, a snap acting U-shaped togglespring continuously biasing said actuator to urge said lever membertoward the iirst position, one side of said toggle spring being incontinuous engagement with said actuator and the other side of saidspring being in pivotal engagement with a tensioned supporting strip,said lever member inclu-ding a force receiving section disposedtransversely within said tube near the other end thereof between saidother end and an adjacent end of the support, one side of said sect-ioncornpressively engaging said other end of the tube at a tirst pivot, theother side of said section compressively engaging said end of thesupport at a second pivot spaced transversely from said iirst pivot,said tube and support being arranged to exert offset and oppositelydirected thermally responsive forces upon said lever member at saidiirst and second pivots respectively to tend to move the pivotslongitudinally in opposite directions and normally urge the lever memberinto the second position against the biasing force of said resilientmeans, the movement of said pivot points upon predetermined temperatureconditions being arranged to allow said resilient means to move saidlever to said iirst position.

12. A thermally responsive switch comprising an elongated tube and anelongated support disposed longitudinally within said tube, said tubeand said support being expansible and contractible longitudinally inresponse to temperature variations with the rate of response of thesupport lagging that of the tube, a lever member disposed within saidtube and operable between -iirst and second positions, an actuatorpivotally mounted upon said support and continuously engaged by saidlever, switch contact means disposed within said tube and operablebetween open and closed positions by said actuator, said switch contactmeans including a movable contact pivotally mounted upon said actuatorand carried thereby, means 4for limiting the free travel of said movablecontact to assure that the contacts will remain in their closed positionunder normal external vibrations, and snap acting resilient meanscontinuously biasing said actuator to urge said lever toward the rstposition, said lever member including a torce receiving section disposedtransversely lwithin said tube, one side of said section engaging saidtube at a iirst pivot, the other side of said section engaging `saidsupport at a second pivot spaced transversely from said first pivot,said tube and support being arranged to exert oiset and oppositelydirected thermally responsive forces upon said lever member at saidtirst and second pivots respectively to tend to move the pivots andnormaily urge the lever member into the second position against thebiasing force of said resilient means, the movement of said pivot pointsupon predetermined temperature conditions being arranged to allow saidresilient means to move said iever to said rst position.

References Cited in the le of this patent UNITED STATES PATENTS1,898,419 Birtch Feb, 2l, 1933 1,983,077 Getchell Dec. 4, 1934 2,664,483Broekhuysen Dec. 29, 1953 2,734,968 Cooper Feb. 14, 1956 2,847,538Bouwman Aug. 12, 1958 FOREIGN PATENTS 815,385 France July l0, 1937

1. A THERMALLY RESPONSIVE SWITCH COMPRISING AN ELONGATED HOUSING, ANELONGATED SUPPORT DISPOSED LONGITUDINALLY WITHIN AND SUBSTANTIALLYCONTAINED BY SAID HOUSING, SAID HOUSING AND SAID SUPPORT EACH BEINGEXPANSIBLE AND CONTRACTIBLE LONGITUDINALLY IN RESPONSE TO TEMPERATUREVARIATIONS AND AT RESPECTIVELY DIFFERENT RATES WITH THE RATE OF RESPONSEOF THE SUPPORT LAGGING THAT OF THE HOUSING, LEVER MEANS DISPOSED WITHINSAID HOUSING AND OPERABLE BETWEEN FIRST AND SECOND POSITIONS, SWITCHCONTACT MEANS DISPOSED WITHIN SAID HOUSING AND OPERABLE BY SAID LEVERMEANS, FIXED CONTACT MEANS ENGAGED BY SAID SWITCH CONTACT MEANS WHENSAID LEVER MEANS IS IN SAID SECOND POSITION, AND RESILIENT MEANSCONTINUOUSLY BIASING SAID LEVER MEANS TOWARD THE FIRST POSITION, SAIDLEVER MEANS INCLUDING A FORCE RECEIVING SECTION DISPOSED TRANSVERSELYWITHIN SAID HOUSING, ONE SIDE OF SAID SECTION ENGAGING SAID HOUSING AT AFIRST PIVOT, THE OTHER SIDE OF SAID SECTION ENGAGING SAID SUPPORT AT ASECOND PIVOT SPACED FROM SAID FIRST PIVOT, SAID HOUSING AND SUPPORTBEING ARRANGED TO EXERT OFFSET AND OPPOSITELY DIRECTED THERMALLYRESPONSIVE FORCES UPON SAID LEVER MEANS AT SAID FIRST AND SECOND PIVOTSRESPECTIVELY TO NORMALLY URGE SAID LEVER MEANS INTO THE SECOND POSITIONAGAINST THE BIASING FORCE OF SAID RESILIENT